How could I access the object from its property in an OOP

Hello,

I Have define two object. On handle object,and another object is beeng passed to the handle object as its properties. Assume like a handle object of Field, which includes some Robot-objects bounded to it as its property. Now, in a method inside the Robot Class I want to access some property of the field, like its dimension. Is there any way which does not includes definning a global variable?

Thank you,

Hadi Hajieghrary

Answer 1

[Abhipsa]

Hello @Hadi Hajieghrary,

I understand that there are two classes involved:

1. A handle class called “Field”, which contains one or more objects of another class called “Robot” as its properties.
2. A class "Robot" that needs, inside one of its methods, to access a property of the “Field” object that contains it.

The query is if there exists a way for a “Robot” object to access the properties of its containing “Field” object from within a method, without using global variables.

You can access properties of the “Field” object from within a method of the “Robot” class without using global variables. The common and clean approach is to have a reference or handle to the “Field” object stored inside each “Robot” object. This way, each “Robot” knows which “Field” it belongs to, and can access the Field’s properties directly.

You can refer to the below code snippet for further reference:

classdef Field < handle
    properties
        Dimension  % Example property
        Robots     % Cell array of Robot objects
    end
    
    methods
        function obj = Field(dim)
            obj.Dimension = dim;
            obj.Robots = {}; % initialize empty
        end
        
        function addRobot(obj, robot)
            robot.ParentField = obj;  % Assign this Field object to Robot
            obj.Robots{end+1} = robot;
        end
    end
end

classdef Robot < handle
    properties
        ParentField  % Reference to the Field object this Robot belongs to
    end
    
    methods
        function obj = Robot()
            % Constructor - can initialize robot-specific things here
        end
        
        function someMethod(obj)
            % Access a property from the Field this robot belongs to
            if ~isempty(obj.ParentField)
                disp(['Field Dimension: ', mat2str(obj.ParentField.Dimension)]);
            else
                disp('This robot has no assigned field.');
            end
        end
    end
end

In the above code snippet:

• “Field” holds many “Robot” objects in its “Robots” property.
• Each “Robot” holds a reference to its parent “Field” in “ParentField”.

This is a classic bidirectional association in object-oriented design which is useful when a "child" object (Robot) needs to query its "Parent" (Field), like checking field dimensions.

You can refer to the below MATLAB documentations for more details:

• Introduction to OOP in MATLAB: https://www.mathworks.com/help/releases/R2024b/matlab/object-oriented-programming.html
• Handle class: https://www.mathworks.com/help/releases/R2024b/matlab/matlab_oop/handle-class-behavior.html
• OOP Best Practices: https://www.mathworks.com/help/releases/R2024b/matlab/matlab_oop/best-practices-for-defining-classes.html

I hope this helps you.